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 $83.31   6.252%   $88.5185   $88.52   $88.50   $88.50  
  Purchase #2 $189.44   4.159%   $197.3188   $197.32   $197.30   $197.30  
  Purchase #3 $25.39   4.191%   $26.4541   $26.45   $26.45   $26.50  
  Purchase #4 $164.27   3.201%   $169.5283   $169.53   $169.55   $169.50  
  Purchase #5 $61.75   6.594%   $65.8218   $65.82   $65.80   $65.80  
  Purchase #6 $205.56   4.301%   $214.4011   $214.40   $214.40   $214.40  
  Purchase #7 $207.50   4.173%   $216.159   $216.16   $216.15   $216.20  
  7 purchase totals = $937.22       $978.2016   $978.20   $978.15   $978.20