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 $180.74   13.397%   $204.9537   $204.95   $204.95   $205.00  
  Purchase #2 $31.48   8.686%   $34.2144   $34.21   $34.20   $34.20  
  Purchase #3 $91.93   12.506%   $103.4268   $103.43   $103.45   $103.40  
  Purchase #4 $188.49   9.408%   $206.2231   $206.22   $206.20   $206.20  
  Purchase #5 $167.30   10.731%   $185.253   $185.25   $185.25   $185.30  
  Purchase #6 $231.90   13.486%   $263.174   $263.17   $263.15   $263.20  
  Purchase #7 $81.52   7.544%   $87.6699   $87.67   $87.65   $87.70  
  7 purchase totals = $973.36       $1,084.9149   $1,084.90   $1,084.85   $1,085.00