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 $62.58   3.838%   $64.9818   $64.98   $65.00   $65.00  
  Purchase #2 $183.31   4.849%   $192.1987   $192.20   $192.20   $192.20  
  Purchase #3 $179.90   6.637%   $191.84   $191.84   $191.85   $191.80  
  Purchase #4 $187.31   12.745%   $211.1827   $211.18   $211.20   $211.20  
  Purchase #5 $232.34   13.432%   $263.5479   $263.55   $263.55   $263.50  
  Purchase #6 $182.90   3.492%   $189.2869   $189.29   $189.30   $189.30  
  Purchase #7 $119.87   7.512%   $128.8746   $128.87   $128.85   $128.90  
  7 purchase totals = $1,148.21       $1,241.9126   $1,241.91   $1,241.95   $1,241.90