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 $203.70   7.530%   $219.0386   $219.04   $219.05   $219.00  
  Purchase #2 $172.31   5.628%   $182.0076   $182.01   $182.00   $182.00  
  Purchase #3 $95.57   7.745%   $102.9719   $102.97   $102.95   $103.00  
  Purchase #4 $192.70   7.760%   $207.6535   $207.65   $207.65   $207.70  
  Purchase #5 $244.60   13.805%   $278.367   $278.37   $278.35   $278.40  
  Purchase #6 $61.60   10.843%   $68.2793   $68.28   $68.30   $68.30  
  Purchase #7 $233.48   12.869%   $263.5265   $263.53   $263.55   $263.50  
  7 purchase totals = $1,203.96       $1,321.8444   $1,321.85   $1,321.85   $1,321.90