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 $149.95   11.425%   $167.0818   $167.08   $167.10   $167.10  
  Purchase #2 $211.68   8.631%   $229.9501   $229.95   $229.95   $230.00  
  Purchase #3 $212.95   4.672%   $222.899   $222.90   $222.90   $222.90  
  Purchase #4 $58.59   6.261%   $62.2583   $62.26   $62.25   $62.30  
  Purchase #5 $244.47   8.184%   $264.4774   $264.48   $264.50   $264.50  
  Purchase #6 $11.68   7.786%   $12.5894   $12.59   $12.60   $12.60  
  Purchase #7 $86.73   3.126%   $89.4412   $89.44   $89.45   $89.40  
  7 purchase totals = $976.05       $1,048.6972   $1,048.70   $1,048.75   $1,048.80