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 $246.28   12.286%   $276.538   $276.54   $276.55   $276.50  
  Purchase #2 $117.49   3.223%   $121.2767   $121.28   $121.30   $121.30  
  Purchase #3 $240.41   10.381%   $265.367   $265.37   $265.35   $265.40  
  Purchase #4 $23.80   5.488%   $25.1061   $25.11   $25.10   $25.10  
  Purchase #5 $31.81   8.651%   $34.5619   $34.56   $34.55   $34.60  
  Purchase #6 $68.87   8.829%   $74.9505   $74.95   $74.95   $75.00  
  Purchase #7 $132.75   12.793%   $149.7327   $149.73   $149.75   $149.70  
  7 purchase totals = $861.41       $947.5329   $947.54   $947.55   $947.60