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 $241.49   12.252%   $271.0774   $271.08   $271.10   $271.10  
  Purchase #2 $244.98   6.174%   $260.1051   $260.11   $260.10   $260.10  
  Purchase #3 $223.96   5.668%   $236.6541   $236.65   $236.65   $236.70  
  Purchase #4 $159.44   3.506%   $165.03   $165.03   $165.05   $165.00  
  Purchase #5 $200.29   6.702%   $213.7134   $213.71   $213.70   $213.70  
  Purchase #6 $183.52   11.229%   $204.1275   $204.13   $204.15   $204.10  
  Purchase #7 $215.67   5.366%   $227.2429   $227.24   $227.25   $227.20  
  7 purchase totals = $1,469.35       $1,577.9504   $1,577.95   $1,578.00   $1,577.90