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 $88.38   9.485%   $96.7628   $96.76   $96.75   $96.80  
  Purchase #2 $101.72   7.508%   $109.3571   $109.36   $109.35   $109.40  
  Purchase #3 $220.39   11.322%   $245.3426   $245.34   $245.35   $245.30  
  Purchase #4 $87.52   8.812%   $95.2323   $95.23   $95.25   $95.20  
  Purchase #5 $221.44   13.473%   $251.2746   $251.27   $251.25   $251.30  
  Purchase #6 $6.81   7.269%   $7.305   $7.31   $7.30   $7.30  
  Purchase #7 $230.93   5.399%   $243.3979   $243.40   $243.40   $243.40  
  7 purchase totals = $957.19       $1,048.6723   $1,048.67   $1,048.65   $1,048.70