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 $187.65   7.390%   $201.5173   $201.52   $201.50   $201.50  
  Purchase #2 $126.72   9.170%   $138.3402   $138.34   $138.35   $138.30  
  Purchase #3 $67.98   12.458%   $76.4489   $76.45   $76.45   $76.40  
  Purchase #4 $204.36   12.544%   $229.9949   $229.99   $230.00   $230.00  
  Purchase #5 $242.70   8.610%   $263.5965   $263.60   $263.60   $263.60  
  Purchase #6 $63.30   11.434%   $70.5377   $70.54   $70.55   $70.50  
  Purchase #7 $29.75   6.457%   $31.671   $31.67   $31.65   $31.70  
  7 purchase totals = $922.46       $1,012.1065   $1,012.11   $1,012.10   $1,012.00