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 $175.43   8.563%   $190.4521   $190.45   $190.45   $190.50  
  Purchase #2 $71.97   12.270%   $80.8007   $80.80   $80.80   $80.80  
  Purchase #3 $39.66   4.748%   $41.5431   $41.54   $41.55   $41.50  
  Purchase #4 $130.47   6.862%   $139.4229   $139.42   $139.40   $139.40  
  Purchase #5 $106.72   8.337%   $115.6172   $115.62   $115.60   $115.60  
  Purchase #6 $17.31   10.427%   $19.1149   $19.11   $19.10   $19.10  
  Purchase #7 $196.79   11.781%   $219.9738   $219.97   $219.95   $220.00  
  7 purchase totals = $738.35       $806.9247   $806.91   $806.85   $806.90