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 $53.25   13.173%   $60.2646   $60.26   $60.25   $60.30  
  Purchase #2 $139.28   11.774%   $155.6788   $155.68   $155.70   $155.70  
  Purchase #3 $36.28   9.622%   $39.7709   $39.77   $39.75   $39.80  
  Purchase #4 $246.49   10.337%   $271.9697   $271.97   $271.95   $272.00  
  Purchase #5 $237.72   12.392%   $267.1783   $267.18   $267.20   $267.20  
  Purchase #6 $102.41   6.122%   $108.6795   $108.68   $108.70   $108.70  
  Purchase #7 $86.71   5.590%   $91.5571   $91.56   $91.55   $91.60  
  7 purchase totals = $902.14       $995.0989   $995.10   $995.10   $995.30