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 $87.38   8.646%   $94.9349   $94.93   $94.95   $94.90  
  Purchase #2 $102.96   5.535%   $108.6588   $108.66   $108.65   $108.70  
  Purchase #3 $169.26   7.241%   $181.5161   $181.52   $181.50   $181.50  
  Purchase #4 $111.63   9.626%   $122.3755   $122.38   $122.40   $122.40  
  Purchase #5 $88.34   4.422%   $92.2464   $92.25   $92.25   $92.20  
  Purchase #6 $75.51   10.623%   $83.5314   $83.53   $83.55   $83.50  
  Purchase #7 $192.61   6.297%   $204.7387   $204.74   $204.75   $204.70  
  7 purchase totals = $827.69       $888.0018   $888.01   $888.05   $887.90