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 $105.78   12.819%   $119.3399   $119.34   $119.35   $119.30  
  Purchase #2 $95.79   4.500%   $100.1006   $100.10   $100.10   $100.10  
  Purchase #3 $246.52   6.795%   $263.271   $263.27   $263.25   $263.30  
  Purchase #4 $171.53   5.223%   $180.489   $180.49   $180.50   $180.50  
  Purchase #5 $14.71   9.470%   $16.103   $16.10   $16.10   $16.10  
  Purchase #6 $8.60   10.716%   $9.5216   $9.52   $9.50   $9.50  
  Purchase #7 $149.55   10.846%   $165.7702   $165.77   $165.75   $165.80  
  7 purchase totals = $792.48       $854.5953   $854.59   $854.55   $854.60