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 $236.87   4.283%   $247.0151   $247.02   $247.00   $247.00  
  Purchase #2 $156.84   9.155%   $171.1987   $171.20   $171.20   $171.20  
  Purchase #3 $82.94   5.270%   $87.3109   $87.31   $87.30   $87.30  
  Purchase #4 $170.97   4.721%   $179.0415   $179.04   $179.05   $179.00  
  Purchase #5 $24.58   7.174%   $26.3434   $26.34   $26.35   $26.30  
  Purchase #6 $242.72   5.173%   $255.2759   $255.28   $255.30   $255.30  
  Purchase #7 $32.77   7.433%   $35.2058   $35.21   $35.20   $35.20  
  7 purchase totals = $947.69       $1,001.3913   $1,001.40   $1,001.40   $1,001.30