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 $191.67   11.716%   $214.1261   $214.13   $214.15   $214.10  
  Purchase #2 $250.57   8.654%   $272.2543   $272.25   $272.25   $272.30  
  Purchase #3 $50.99   10.417%   $56.3016   $56.30   $56.30   $56.30  
  Purchase #4 $228.45   6.801%   $243.9869   $243.99   $244.00   $244.00  
  Purchase #5 $135.35   12.792%   $152.664   $152.66   $152.65   $152.70  
  Purchase #6 $23.86   5.483%   $25.1682   $25.17   $25.15   $25.20  
  Purchase #7 $243.29   10.451%   $268.7162   $268.72   $268.70   $268.70  
  7 purchase totals = $1,124.18       $1,233.2173   $1,233.22   $1,233.20   $1,233.30