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 $61.58   9.460%   $67.4055   $67.41   $67.40   $67.40  
  Purchase #2 $180.29   13.216%   $204.1171   $204.12   $204.10   $204.10  
  Purchase #3 $58.97   12.153%   $66.1366   $66.14   $66.15   $66.10  
  Purchase #4 $206.89   3.707%   $214.5594   $214.56   $214.55   $214.60  
  Purchase #5 $199.44   11.764%   $222.9021   $222.90   $222.90   $222.90  
  Purchase #6 $239.54   3.184%   $247.167   $247.17   $247.15   $247.20  
  Purchase #7 $63.98   12.295%   $71.8463   $71.85   $71.85   $71.80  
  7 purchase totals = $1,010.69       $1,094.1340   $1,094.15   $1,094.10   $1,094.10