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 $96.95   4.822%   $101.6249   $101.62   $101.60   $101.60  
  Purchase #2 $166.99   9.607%   $183.0327   $183.03   $183.05   $183.00  
  Purchase #3 $65.98   13.346%   $74.7857   $74.79   $74.80   $74.80  
  Purchase #4 $44.51   9.437%   $48.7104   $48.71   $48.70   $48.70  
  Purchase #5 $245.30   7.760%   $264.3353   $264.34   $264.35   $264.30  
  Purchase #6 $179.77   12.462%   $202.1729   $202.17   $202.15   $202.20  
  Purchase #7 $53.29   6.628%   $56.8221   $56.82   $56.80   $56.80  
  7 purchase totals = $852.79       $931.4840   $931.48   $931.45   $931.40