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 $90.49   6.733%   $96.5827   $96.58   $96.60   $96.60  
  Purchase #2 $116.31   5.654%   $122.8862   $122.89   $122.90   $122.90  
  Purchase #3 $67.90   9.202%   $74.1482   $74.15   $74.15   $74.10  
  Purchase #4 $222.82   7.761%   $240.1131   $240.11   $240.10   $240.10  
  Purchase #5 $112.32   5.324%   $118.2999   $118.30   $118.30   $118.30  
  Purchase #6 $244.32   7.791%   $263.355   $263.36   $263.35   $263.40  
  Purchase #7 $138.73   6.170%   $147.2896   $147.29   $147.30   $147.30  
  7 purchase totals = $992.89       $1,062.6747   $1,062.68   $1,062.70   $1,062.70