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 $179.97   8.635%   $195.5104   $195.51   $195.50   $195.50  
  Purchase #2 $160.79   8.264%   $174.0777   $174.08   $174.10   $174.10  
  Purchase #3 $109.61   12.404%   $123.206   $123.21   $123.20   $123.20  
  Purchase #4 $176.96   9.113%   $193.0864   $193.09   $193.10   $193.10  
  Purchase #5 $167.49   9.248%   $182.9795   $182.98   $183.00   $183.00  
  Purchase #6 $34.95   9.628%   $38.315   $38.32   $38.30   $38.30  
  Purchase #7 $110.31   5.431%   $116.3009   $116.30   $116.30   $116.30  
  7 purchase totals = $940.08       $1,023.4759   $1,023.49   $1,023.50   $1,023.50