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 $246.29   11.361%   $274.271   $274.27   $274.25   $274.30  
  Purchase #2 $136.25   10.261%   $150.2306   $150.23   $150.25   $150.20  
  Purchase #3 $48.77   10.364%   $53.8245   $53.82   $53.80   $53.80  
  Purchase #4 $226.39   8.320%   $245.2256   $245.23   $245.25   $245.20  
  Purchase #5 $186.27   12.357%   $209.2874   $209.29   $209.30   $209.30  
  Purchase #6 $193.94   3.651%   $201.0207   $201.02   $201.00   $201.00  
  Purchase #7 $36.67   7.313%   $39.3517   $39.35   $39.35   $39.40  
  7 purchase totals = $1,074.58       $1,173.2115   $1,173.21   $1,173.20   $1,173.20