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 $60.65   11.106%   $67.3858   $67.39   $67.40   $67.40  
  Purchase #2 $210.47   9.103%   $229.6291   $229.63   $229.65   $229.60  
  Purchase #3 $212.92   6.800%   $227.3986   $227.40   $227.40   $227.40  
  Purchase #4 $193.73   6.313%   $205.9602   $205.96   $205.95   $206.00  
  Purchase #5 $26.82   8.142%   $29.0037   $29.00   $29.00   $29.00  
  Purchase #6 $45.32   10.521%   $50.0881   $50.09   $50.10   $50.10  
  Purchase #7 $181.53   11.870%   $203.0776   $203.08   $203.10   $203.10  
  7 purchase totals = $931.44       $1,012.5431   $1,012.55   $1,012.60   $1,012.60