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 $61.81   10.588%   $68.3544   $68.35   $68.35   $68.40  
  Purchase #2 $151.70   10.387%   $167.4571   $167.46   $167.45   $167.50  
  Purchase #3 $27.26   3.398%   $28.1863   $28.19   $28.20   $28.20  
  Purchase #4 $215.62   12.495%   $242.5617   $242.56   $242.55   $242.60  
  Purchase #5 $223.79   5.440%   $235.9642   $235.96   $235.95   $236.00  
  Purchase #6 $150.50   13.763%   $171.2133   $171.21   $171.20   $171.20  
  Purchase #7 $129.49   5.816%   $137.0211   $137.02   $137.00   $137.00  
  7 purchase totals = $960.17       $1,050.7581   $1,050.75   $1,050.70   $1,050.90