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 $234.28   12.545%   $263.6704   $263.67   $263.65   $263.70  
  Purchase #2 $35.99   8.870%   $39.1823   $39.18   $39.20   $39.20  
  Purchase #3 $161.54   12.452%   $181.655   $181.66   $181.65   $181.70  
  Purchase #4 $214.65   11.204%   $238.6994   $238.70   $238.70   $238.70  
  Purchase #5 $130.43   6.519%   $138.9327   $138.93   $138.95   $138.90  
  Purchase #6 $206.86   9.533%   $226.58   $226.58   $226.60   $226.60  
  Purchase #7 $96.35   6.274%   $102.395   $102.40   $102.40   $102.40  
  7 purchase totals = $1,080.10       $1,191.1148   $1,191.12   $1,191.15   $1,191.20