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 $57.71   5.711%   $61.0058   $61.01   $61.00   $61.00  
  Purchase #2 $160.55   6.373%   $170.7819   $170.78   $170.80   $170.80  
  Purchase #3 $170.86   7.399%   $183.5019   $183.50   $183.50   $183.50  
  Purchase #4 $119.75   7.816%   $129.1097   $129.11   $129.10   $129.10  
  Purchase #5 $31.33   9.509%   $34.3092   $34.31   $34.30   $34.30  
  Purchase #6 $187.35   9.376%   $204.9159   $204.92   $204.90   $204.90  
  Purchase #7 $209.71   9.866%   $230.4   $230.40   $230.40   $230.40  
  7 purchase totals = $937.26       $1,014.0244   $1,014.03   $1,014.00   $1,014.00