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 $145.39   4.740%   $152.2815   $152.28   $152.30   $152.30  
  Purchase #2 $241.76   5.258%   $254.4717   $254.47   $254.45   $254.50  
  Purchase #3 $160.59   10.733%   $177.8261   $177.83   $177.85   $177.80  
  Purchase #4 $219.69   11.614%   $245.2048   $245.20   $245.20   $245.20  
  Purchase #5 $58.85   5.574%   $62.1303   $62.13   $62.15   $62.10  
  Purchase #6 $74.28   11.378%   $82.7316   $82.73   $82.75   $82.70  
  Purchase #7 $158.57   5.299%   $166.9726   $166.97   $166.95   $167.00  
  7 purchase totals = $1,059.13       $1,141.6186   $1,141.61   $1,141.65   $1,141.60