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 $213.70   10.303%   $235.7175   $235.72   $235.70   $235.70  
  Purchase #2 $205.93   7.108%   $220.5675   $220.57   $220.55   $220.60  
  Purchase #3 $46.31   4.867%   $48.5639   $48.56   $48.55   $48.60  
  Purchase #4 $187.61   8.454%   $203.4705   $203.47   $203.45   $203.50  
  Purchase #5 $249.38   10.475%   $275.5026   $275.50   $275.50   $275.50  
  Purchase #6 $53.58   13.773%   $60.9596   $60.96   $60.95   $61.00  
  Purchase #7 $207.67   10.760%   $230.0153   $230.02   $230.00   $230.00  
  7 purchase totals = $1,164.18       $1,274.7969   $1,274.80   $1,274.70   $1,274.90