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 $88.59   6.853%   $94.6611   $94.66   $94.65   $94.70  
  Purchase #2 $134.63   11.753%   $150.4531   $150.45   $150.45   $150.50  
  Purchase #3 $88.50   12.302%   $99.3873   $99.39   $99.40   $99.40  
  Purchase #4 $35.67   11.442%   $39.7514   $39.75   $39.75   $39.80  
  Purchase #5 $200.76   5.453%   $211.7074   $211.71   $211.70   $211.70  
  Purchase #6 $179.70   13.721%   $204.3566   $204.36   $204.35   $204.40  
  Purchase #7 $181.30   9.349%   $198.2497   $198.25   $198.25   $198.20  
  7 purchase totals = $909.15       $998.5666   $998.57   $998.55   $998.70