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 $26.75   11.121%   $29.7249   $29.72   $29.70   $29.70  
  Purchase #2 $217.99   5.814%   $230.6639   $230.66   $230.65   $230.70  
  Purchase #3 $202.35   12.628%   $227.9028   $227.90   $227.90   $227.90  
  Purchase #4 $62.65   8.755%   $68.135   $68.14   $68.15   $68.10  
  Purchase #5 $165.85   8.113%   $179.3054   $179.31   $179.30   $179.30  
  Purchase #6 $144.60   3.687%   $149.9314   $149.93   $149.95   $149.90  
  Purchase #7 $111.64   5.414%   $117.6842   $117.68   $117.70   $117.70  
  7 purchase totals = $931.83       $1,003.3476   $1,003.34   $1,003.35   $1,003.30