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 $154.94   12.782%   $174.7444   $174.74   $174.75   $174.70  
  Purchase #2 $103.60   12.310%   $116.3532   $116.35   $116.35   $116.40  
  Purchase #3 $159.87   8.163%   $172.9202   $172.92   $172.90   $172.90  
  Purchase #4 $106.58   10.709%   $117.9937   $117.99   $118.00   $118.00  
  Purchase #5 $214.57   13.486%   $243.5069   $243.51   $243.50   $243.50  
  Purchase #6 $76.53   9.550%   $83.8386   $83.84   $83.85   $83.80  
  Purchase #7 $155.96   12.319%   $175.1727   $175.17   $175.15   $175.20  
  7 purchase totals = $972.05       $1,084.5297   $1,084.52   $1,084.50   $1,084.50