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 $89.48   7.830%   $96.4863   $96.49   $96.50   $96.50  
  Purchase #2 $170.74   11.653%   $190.6363   $190.64   $190.65   $190.60  
  Purchase #3 $22.57   7.319%   $24.2219   $24.22   $24.20   $24.20  
  Purchase #4 $102.64   6.621%   $109.4358   $109.44   $109.45   $109.40  
  Purchase #5 $48.70   6.645%   $51.9361   $51.94   $51.95   $51.90  
  Purchase #6 $203.26   7.772%   $219.0574   $219.06   $219.05   $219.10  
  Purchase #7 $96.73   6.345%   $102.8675   $102.87   $102.85   $102.90  
  7 purchase totals = $734.12       $794.6413   $794.66   $794.65   $794.60