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 $31.33   6.415%   $33.3398   $33.34   $33.35   $33.30  
  Purchase #2 $191.98   11.126%   $213.3397   $213.34   $213.35   $213.30  
  Purchase #3 $56.81   11.224%   $63.1864   $63.19   $63.20   $63.20  
  Purchase #4 $69.74   3.304%   $72.0442   $72.04   $72.05   $72.00  
  Purchase #5 $175.49   10.800%   $194.4429   $194.44   $194.45   $194.40  
  Purchase #6 $187.94   10.628%   $207.9143   $207.91   $207.90   $207.90  
  Purchase #7 $212.58   3.164%   $219.306   $219.31   $219.30   $219.30  
  7 purchase totals = $925.87       $1,003.5733   $1,003.57   $1,003.60   $1,003.40