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 $83.88   12.124%   $94.0496   $94.05   $94.05   $94.00  
  Purchase #2 $49.52   8.767%   $53.8614   $53.86   $53.85   $53.90  
  Purchase #3 $64.55   9.381%   $70.6054   $70.61   $70.60   $70.60  
  Purchase #4 $232.79   4.158%   $242.4694   $242.47   $242.45   $242.50  
  Purchase #5 $23.77   7.352%   $25.5176   $25.52   $25.50   $25.50  
  Purchase #6 $31.95   9.274%   $34.913   $34.91   $34.90   $34.90  
  Purchase #7 $184.39   10.154%   $203.113   $203.11   $203.10   $203.10  
  7 purchase totals = $670.85       $724.5294   $724.53   $724.45   $724.50