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 $204.84   13.717%   $232.9379   $232.94   $232.95   $232.90  
  Purchase #2 $36.82   8.437%   $39.9265   $39.93   $39.95   $39.90  
  Purchase #3 $31.93   3.519%   $33.0536   $33.05   $33.05   $33.10  
  Purchase #4 $202.88   11.787%   $226.7935   $226.79   $226.80   $226.80  
  Purchase #5 $131.76   12.363%   $148.0495   $148.05   $148.05   $148.00  
  Purchase #6 $193.59   6.487%   $206.1482   $206.15   $206.15   $206.10  
  Purchase #7 $196.99   5.184%   $207.202   $207.20   $207.20   $207.20  
  7 purchase totals = $998.81       $1,094.1112   $1,094.11   $1,094.15   $1,094.00