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 $88.78   10.788%   $98.3576   $98.36   $98.35   $98.40  
  Purchase #2 $196.31   10.154%   $216.2433   $216.24   $216.25   $216.20  
  Purchase #3 $82.66   10.351%   $91.2161   $91.22   $91.20   $91.20  
  Purchase #4 $66.38   12.319%   $74.5574   $74.56   $74.55   $74.60  
  Purchase #5 $27.63   13.764%   $31.433   $31.43   $31.45   $31.40  
  Purchase #6 $200.92   12.271%   $225.5749   $225.57   $225.55   $225.60  
  Purchase #7 $219.26   5.353%   $230.997   $231.00   $231.00   $231.00  
  7 purchase totals = $881.94       $968.3793   $968.38   $968.35   $968.40