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 $125.63   6.663%   $134.0007   $134.00   $134.00   $134.00  
  Purchase #2 $226.92   8.764%   $246.8073   $246.81   $246.80   $246.80  
  Purchase #3 $226.92   6.421%   $241.4905   $241.49   $241.50   $241.50  
  Purchase #4 $85.60   9.753%   $93.9486   $93.95   $93.95   $93.90  
  Purchase #5 $146.28   11.747%   $163.4635   $163.46   $163.45   $163.50  
  Purchase #6 $138.84   8.453%   $150.5761   $150.58   $150.60   $150.60  
  Purchase #7 $20.75   5.722%   $21.9373   $21.94   $21.95   $21.90  
  7 purchase totals = $970.94       $1,052.2240   $1,052.23   $1,052.25   $1,052.20