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 $204.74   7.217%   $219.5161   $219.52   $219.50   $219.50  
  Purchase #2 $25.68   11.247%   $28.5682   $28.57   $28.55   $28.60  
  Purchase #3 $46.80   8.832%   $50.9334   $50.93   $50.95   $50.90  
  Purchase #4 $210.32   9.399%   $230.088   $230.09   $230.10   $230.10  
  Purchase #5 $146.49   12.284%   $164.4848   $164.48   $164.50   $164.50  
  Purchase #6 $128.73   12.163%   $144.3874   $144.39   $144.40   $144.40  
  Purchase #7 $156.96   8.848%   $170.8478   $170.85   $170.85   $170.80  
  7 purchase totals = $919.72       $1,008.8257   $1,008.83   $1,008.85   $1,008.80