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 $158.72   10.271%   $175.0221   $175.02   $175.00   $175.00  
  Purchase #2 $197.45   3.504%   $204.3686   $204.37   $204.35   $204.40  
  Purchase #3 $35.87   7.390%   $38.5208   $38.52   $38.50   $38.50  
  Purchase #4 $25.32   8.254%   $27.4099   $27.41   $27.40   $27.40  
  Purchase #5 $57.35   6.500%   $61.0778   $61.08   $61.10   $61.10  
  Purchase #6 $166.28   8.731%   $180.7979   $180.80   $180.80   $180.80  
  Purchase #7 $151.61   10.486%   $167.5078   $167.51   $167.50   $167.50  
  7 purchase totals = $792.60       $854.7049   $854.71   $854.65   $854.70