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 $233.65   13.470%   $265.1227   $265.12   $265.10   $265.10  
  Purchase #2 $217.33   4.789%   $227.7379   $227.74   $227.75   $227.70  
  Purchase #3 $33.28   10.647%   $36.8233   $36.82   $36.80   $36.80  
  Purchase #4 $96.91   7.511%   $104.1889   $104.19   $104.20   $104.20  
  Purchase #5 $250.56   6.836%   $267.6883   $267.69   $267.70   $267.70  
  Purchase #6 $128.35   11.112%   $142.6123   $142.61   $142.60   $142.60  
  Purchase #7 $14.80   10.594%   $16.3679   $16.37   $16.35   $16.40  
  7 purchase totals = $974.88       $1,060.5413   $1,060.54   $1,060.50   $1,060.50