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 $84.49   4.136%   $87.9845   $87.98   $88.00   $88.00  
  Purchase #2 $118.57   4.226%   $123.5808   $123.58   $123.60   $123.60  
  Purchase #3 $163.74   8.474%   $177.6153   $177.62   $177.60   $177.60  
  Purchase #4 $187.88   3.673%   $194.7808   $194.78   $194.80   $194.80  
  Purchase #5 $218.52   6.204%   $232.077   $232.08   $232.10   $232.10  
  Purchase #6 $195.31   10.132%   $215.0988   $215.10   $215.10   $215.10  
  Purchase #7 $250.82   4.657%   $262.5007   $262.50   $262.50   $262.50  
  7 purchase totals = $1,219.33       $1,293.6379   $1,293.64   $1,293.70   $1,293.70