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 $74.53   12.506%   $83.8507   $83.85   $83.85   $83.90  
  Purchase #2 $182.96   3.672%   $189.6783   $189.68   $189.70   $189.70  
  Purchase #3 $226.36   9.119%   $247.0018   $247.00   $247.00   $247.00  
  Purchase #4 $205.39   12.780%   $231.6388   $231.64   $231.65   $231.60  
  Purchase #5 $241.83   4.134%   $251.8273   $251.83   $251.85   $251.80  
  Purchase #6 $192.57   10.506%   $212.8014   $212.80   $212.80   $212.80  
  Purchase #7 $136.85   3.853%   $142.1228   $142.12   $142.10   $142.10  
  7 purchase totals = $1,260.49       $1,358.9211   $1,358.92   $1,358.95   $1,358.90