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 $78.51   10.779%   $86.9726   $86.97   $86.95   $87.00  
  Purchase #2 $179.93   6.675%   $191.9403   $191.94   $191.95   $191.90  
  Purchase #3 $125.93   6.722%   $134.395   $134.40   $134.40   $134.40  
  Purchase #4 $181.91   7.201%   $195.0093   $195.01   $195.00   $195.00  
  Purchase #5 $121.56   3.537%   $125.8596   $125.86   $125.85   $125.90  
  Purchase #6 $125.35   13.804%   $142.6533   $142.65   $142.65   $142.70  
  Purchase #7 $161.30   11.277%   $179.4898   $179.49   $179.50   $179.50  
  7 purchase totals = $974.49       $1,056.3199   $1,056.32   $1,056.30   $1,056.40