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 $148.79   13.115%   $168.3038   $168.30   $168.30   $168.30  
  Purchase #2 $211.82   9.319%   $231.5595   $231.56   $231.55   $231.60  
  Purchase #3 $65.40   10.245%   $72.1002   $72.10   $72.10   $72.10  
  Purchase #4 $88.96   7.225%   $95.3874   $95.39   $95.40   $95.40  
  Purchase #5 $120.62   9.538%   $132.1247   $132.12   $132.10   $132.10  
  Purchase #6 $24.38   9.193%   $26.6213   $26.62   $26.60   $26.60  
  Purchase #7 $212.51   10.820%   $235.5036   $235.50   $235.50   $235.50  
  7 purchase totals = $872.48       $961.6005   $961.59   $961.55   $961.60