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 $21.42   4.406%   $22.3638   $22.36   $22.35   $22.40  
  Purchase #2 $74.56   10.524%   $82.4067   $82.41   $82.40   $82.40  
  Purchase #3 $15.37   9.504%   $16.8308   $16.83   $16.85   $16.80  
  Purchase #4 $204.35   13.244%   $231.4141   $231.41   $231.40   $231.40  
  Purchase #5 $194.72   10.424%   $215.0176   $215.02   $215.00   $215.00  
  Purchase #6 $170.64   10.141%   $187.9446   $187.94   $187.95   $187.90  
  Purchase #7 $245.88   11.480%   $274.107   $274.11   $274.10   $274.10  
  7 purchase totals = $926.94       $1,030.0846   $1,030.08   $1,030.05   $1,030.00