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 $204.52   10.797%   $226.602   $226.60   $226.60   $226.60  
  Purchase #2 $20.96   9.293%   $22.9078   $22.91   $22.90   $22.90  
  Purchase #3 $165.56   12.286%   $185.9007   $185.90   $185.90   $185.90  
  Purchase #4 $93.89   13.704%   $106.7567   $106.76   $106.75   $106.80  
  Purchase #5 $41.41   5.397%   $43.6449   $43.64   $43.65   $43.60  
  Purchase #6 $192.69   5.862%   $203.9855   $203.99   $204.00   $204.00  
  Purchase #7 $121.51   5.729%   $128.4713   $128.47   $128.45   $128.50  
  7 purchase totals = $840.54       $918.2689   $918.27   $918.25   $918.30