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 $118.72   12.265%   $133.281   $133.28   $133.30   $133.30  
  Purchase #2 $162.70   6.339%   $173.0136   $173.01   $173.00   $173.00  
  Purchase #3 $68.34   7.753%   $73.6384   $73.64   $73.65   $73.60  
  Purchase #4 $234.71   5.572%   $247.788   $247.79   $247.80   $247.80  
  Purchase #5 $104.85   5.685%   $110.8107   $110.81   $110.80   $110.80  
  Purchase #6 $212.55   7.740%   $229.0014   $229.00   $229.00   $229.00  
  Purchase #7 $42.59   10.755%   $47.1706   $47.17   $47.15   $47.20  
  7 purchase totals = $944.46       $1,014.7037   $1,014.70   $1,014.70   $1,014.70