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 $119.77   12.683%   $134.9604   $134.96   $134.95   $135.00  
  Purchase #2 $186.95   9.162%   $204.0784   $204.08   $204.10   $204.10  
  Purchase #3 $212.98   13.488%   $241.7067   $241.71   $241.70   $241.70  
  Purchase #4 $110.45   6.485%   $117.6127   $117.61   $117.60   $117.60  
  Purchase #5 $203.94   4.688%   $213.5007   $213.50   $213.50   $213.50  
  Purchase #6 $61.51   11.412%   $68.5295   $68.53   $68.55   $68.50  
  Purchase #7 $83.27   12.814%   $93.9402   $93.94   $93.95   $93.90  
  7 purchase totals = $978.87       $1,074.3286   $1,074.33   $1,074.35   $1,074.30