Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $204.84   12.551%   $230.5495   $230.55   $230.55   $230.50  
  Purchase #2 $173.86   9.144%   $189.7578   $189.76   $189.75   $189.80  
  Purchase #3 $167.37   7.292%   $179.5746   $179.57   $179.55   $179.60  
  Purchase #4 $211.85   12.358%   $238.0304   $238.03   $238.05   $238.00  
  Purchase #5 $231.97   6.605%   $247.2916   $247.29   $247.30   $247.30  
  Purchase #6 $147.29   7.420%   $158.2189   $158.22   $158.20   $158.20  
  Purchase #7 $193.31   5.266%   $203.4897   $203.49   $203.50   $203.50  
  7 purchase totals = $1,330.49       $1,446.9125   $1,446.91   $1,446.90   $1,446.90