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 $173.97   13.710%   $197.8213   $197.82   $197.80   $197.80  
  Purchase #2 $249.84   10.858%   $276.9676   $276.97   $276.95   $277.00  
  Purchase #3 $166.64   3.452%   $172.3924   $172.39   $172.40   $172.40  
  Purchase #4 $26.96   9.625%   $29.5549   $29.55   $29.55   $29.60  
  Purchase #5 $81.80   4.850%   $85.7673   $85.77   $85.75   $85.80  
  Purchase #6 $200.59   8.576%   $217.7926   $217.79   $217.80   $217.80  
  Purchase #7 $60.60   8.312%   $65.6371   $65.64   $65.65   $65.60  
  7 purchase totals = $960.40       $1,045.9332   $1,045.93   $1,045.90   $1,046.00