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 $94.30   13.662%   $107.1833   $107.18   $107.20   $107.20  
  Purchase #2 $84.83   12.292%   $95.2573   $95.26   $95.25   $95.30  
  Purchase #3 $189.78   4.841%   $198.9672   $198.97   $198.95   $199.00  
  Purchase #4 $207.99   10.706%   $230.2574   $230.26   $230.25   $230.30  
  Purchase #5 $191.53   5.566%   $202.1906   $202.19   $202.20   $202.20  
  Purchase #6 $172.89   5.227%   $181.927   $181.93   $181.95   $181.90  
  Purchase #7 $228.66   11.447%   $254.8347   $254.83   $254.85   $254.80  
  7 purchase totals = $1,169.98       $1,270.6175   $1,270.62   $1,270.65   $1,270.70