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 $204.28   7.501%   $219.603   $219.60   $219.60   $219.60  
  Purchase #2 $101.29   5.217%   $106.5743   $106.57   $106.55   $106.60  
  Purchase #3 $39.55   8.791%   $43.0268   $43.03   $43.05   $43.00  
  Purchase #4 $124.63   12.451%   $140.1477   $140.15   $140.15   $140.10  
  Purchase #5 $102.97   7.466%   $110.6577   $110.66   $110.65   $110.70  
  Purchase #6 $201.88   8.349%   $218.735   $218.74   $218.75   $218.70  
  Purchase #7 $52.82   11.301%   $58.7892   $58.79   $58.80   $58.80  
  7 purchase totals = $827.42       $897.5337   $897.54   $897.55   $897.50