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 $120.85   9.351%   $132.1507   $132.15   $132.15   $132.20  
  Purchase #2 $71.48   12.131%   $80.1512   $80.15   $80.15   $80.20  
  Purchase #3 $222.42   13.145%   $251.6571   $251.66   $251.65   $251.70  
  Purchase #4 $226.47   3.647%   $234.7294   $234.73   $234.75   $234.70  
  Purchase #5 $189.84   7.573%   $204.2166   $204.22   $204.20   $204.20  
  Purchase #6 $212.86   6.522%   $226.7427   $226.74   $226.75   $226.70  
  Purchase #7 $118.81   4.580%   $124.2515   $124.25   $124.25   $124.30  
  7 purchase totals = $1,162.73       $1,253.8992   $1,253.90   $1,253.90   $1,254.00