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 $12.67   12.130%   $14.2069   $14.21   $14.20   $14.20  
  Purchase #2 $235.92   5.191%   $248.1666   $248.17   $248.15   $248.20  
  Purchase #3 $55.70   11.632%   $62.179   $62.18   $62.20   $62.20  
  Purchase #4 $176.64   10.727%   $195.5882   $195.59   $195.60   $195.60  
  Purchase #5 $210.49   10.192%   $231.9431   $231.94   $231.95   $231.90  
  Purchase #6 $170.57   6.183%   $181.1163   $181.12   $181.10   $181.10  
  Purchase #7 $123.29   8.129%   $133.3122   $133.31   $133.30   $133.30  
  7 purchase totals = $985.28       $1,066.5123   $1,066.52   $1,066.50   $1,066.50