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 $53.42   13.190%   $60.4661   $60.47   $60.45   $60.50  
  Purchase #2 $117.87   5.821%   $124.7312   $124.73   $124.75   $124.70  
  Purchase #3 $175.45   9.166%   $191.5317   $191.53   $191.55   $191.50  
  Purchase #4 $175.83   9.170%   $191.9536   $191.95   $191.95   $192.00  
  Purchase #5 $202.77   12.764%   $228.6516   $228.65   $228.65   $228.70  
  Purchase #6 $224.35   3.482%   $232.1619   $232.16   $232.15   $232.20  
  Purchase #7 $25.72   10.525%   $28.427   $28.43   $28.45   $28.40  
  7 purchase totals = $975.41       $1,057.9231   $1,057.92   $1,057.95   $1,058.00