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 $172.39   7.154%   $184.7228   $184.72   $184.70   $184.70  
  Purchase #2 $230.80   6.739%   $246.3536   $246.35   $246.35   $246.40  
  Purchase #3 $178.25   11.866%   $199.4011   $199.40   $199.40   $199.40  
  Purchase #4 $63.40   13.660%   $72.0604   $72.06   $72.05   $72.10  
  Purchase #5 $52.56   5.428%   $55.413   $55.41   $55.40   $55.40  
  Purchase #6 $235.40   9.464%   $257.6783   $257.68   $257.70   $257.70  
  Purchase #7 $29.40   8.571%   $31.9199   $31.92   $31.90   $31.90  
  7 purchase totals = $962.20       $1,047.5491   $1,047.54   $1,047.50   $1,047.60