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 $162.52   9.397%   $177.792   $177.79   $177.80   $177.80  
  Purchase #2 $25.68   8.853%   $27.9535   $27.95   $27.95   $28.00  
  Purchase #3 $71.63   7.205%   $76.7909   $76.79   $76.80   $76.80  
  Purchase #4 $71.96   11.405%   $80.167   $80.17   $80.15   $80.20  
  Purchase #5 $74.70   11.751%   $83.478   $83.48   $83.50   $83.50  
  Purchase #6 $76.45   12.726%   $86.179   $86.18   $86.20   $86.20  
  Purchase #7 $219.32   3.443%   $226.8712   $226.87   $226.85   $226.90  
  7 purchase totals = $702.26       $759.2316   $759.23   $759.25   $759.40