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 $202.67   7.623%   $218.1195   $218.12   $218.10   $218.10  
  Purchase #2 $67.46   12.149%   $75.6557   $75.66   $75.65   $75.70  
  Purchase #3 $68.40   7.453%   $73.4979   $73.50   $73.50   $73.50  
  Purchase #4 $231.84   4.187%   $241.5471   $241.55   $241.55   $241.50  
  Purchase #5 $230.92   6.656%   $246.29   $246.29   $246.30   $246.30  
  Purchase #6 $178.89   11.708%   $199.8344   $199.83   $199.85   $199.80  
  Purchase #7 $73.44   13.663%   $83.4741   $83.47   $83.45   $83.50  
  7 purchase totals = $1,053.62       $1,138.4187   $1,138.42   $1,138.40   $1,138.40