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 $84.81   9.312%   $92.7075   $92.71   $92.70   $92.70  
  Purchase #2 $147.52   3.344%   $152.4531   $152.45   $152.45   $152.50  
  Purchase #3 $134.25   7.481%   $144.2932   $144.29   $144.30   $144.30  
  Purchase #4 $204.92   5.663%   $216.5246   $216.52   $216.50   $216.50  
  Purchase #5 $201.96   9.270%   $220.6817   $220.68   $220.70   $220.70  
  Purchase #6 $244.50   4.684%   $255.9524   $255.95   $255.95   $256.00  
  Purchase #7 $219.78   13.317%   $249.0481   $249.05   $249.05   $249.00  
  7 purchase totals = $1,237.74       $1,331.6606   $1,331.65   $1,331.65   $1,331.70