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 $49.67   8.650%   $53.9665   $53.97   $53.95   $54.00  
  Purchase #2 $167.78   10.106%   $184.7358   $184.74   $184.75   $184.70  
  Purchase #3 $202.98   5.674%   $214.4971   $214.50   $214.50   $214.50  
  Purchase #4 $119.84   12.801%   $135.1807   $135.18   $135.20   $135.20  
  Purchase #5 $139.87   12.222%   $156.9649   $156.96   $156.95   $157.00  
  Purchase #6 $156.84   8.494%   $170.162   $170.16   $170.15   $170.20  
  Purchase #7 $89.77   10.845%   $99.5056   $99.51   $99.50   $99.50  
  7 purchase totals = $926.75       $1,015.0126   $1,015.02   $1,015.00   $1,015.10