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 $55.33   6.269%   $58.7986   $58.80   $58.80   $58.80  
  Purchase #2 $134.45   9.597%   $147.3532   $147.35   $147.35   $147.40  
  Purchase #3 $247.87   5.779%   $262.1944   $262.19   $262.20   $262.20  
  Purchase #4 $120.96   8.301%   $131.0009   $131.00   $131.00   $131.00  
  Purchase #5 $231.35   8.731%   $251.5492   $251.55   $251.55   $251.50  
  Purchase #6 $241.89   8.736%   $263.0215   $263.02   $263.00   $263.00  
  Purchase #7 $181.48   12.457%   $204.087   $204.09   $204.10   $204.10  
  7 purchase totals = $1,213.33       $1,318.0048   $1,318.00   $1,318.00   $1,318.00