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 $148.52   11.773%   $166.0053   $166.01   $166.00   $166.00  
  Purchase #2 $183.46   10.277%   $202.3142   $202.31   $202.30   $202.30  
  Purchase #3 $172.97   12.707%   $194.9493   $194.95   $194.95   $194.90  
  Purchase #4 $200.41   10.775%   $222.0042   $222.00   $222.00   $222.00  
  Purchase #5 $76.92   6.548%   $81.9567   $81.96   $81.95   $82.00  
  Purchase #6 $45.43   5.196%   $47.7905   $47.79   $47.80   $47.80  
  Purchase #7 $124.46   4.459%   $130.0097   $130.01   $130.00   $130.00  
  7 purchase totals = $952.17       $1,045.0299   $1,045.03   $1,045.00   $1,045.00