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 $94.93   8.610%   $103.1035   $103.10   $103.10   $103.10  
  Purchase #2 $198.26   9.639%   $217.3703   $217.37   $217.35   $217.40  
  Purchase #3 $221.84   9.739%   $243.445   $243.45   $243.45   $243.40  
  Purchase #4 $79.96   7.426%   $85.8978   $85.90   $85.90   $85.90  
  Purchase #5 $125.84   3.385%   $130.0997   $130.10   $130.10   $130.10  
  Purchase #6 $177.38   11.219%   $197.2803   $197.28   $197.30   $197.30  
  Purchase #7 $43.88   8.342%   $47.5405   $47.54   $47.55   $47.50  
  7 purchase totals = $942.09       $1,024.7371   $1,024.74   $1,024.75   $1,024.70