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 $95.95   11.241%   $106.7357   $106.74   $106.75   $106.70  
  Purchase #2 $160.26   9.408%   $175.3373   $175.34   $175.35   $175.30  
  Purchase #3 $171.77   7.672%   $184.9482   $184.95   $184.95   $184.90  
  Purchase #4 $212.32   7.651%   $228.5646   $228.56   $228.55   $228.60  
  Purchase #5 $67.46   8.674%   $73.3115   $73.31   $73.30   $73.30  
  Purchase #6 $177.74   5.185%   $186.9558   $186.96   $186.95   $187.00  
  Purchase #7 $39.55   4.193%   $41.2083   $41.21   $41.20   $41.20  
  7 purchase totals = $925.05       $997.0614   $997.07   $997.05   $997.00