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 $213.91   13.122%   $241.9793   $241.98   $242.00   $242.00  
  Purchase #2 $164.85   4.728%   $172.6441   $172.64   $172.65   $172.60  
  Purchase #3 $107.31   9.362%   $117.3564   $117.36   $117.35   $117.40  
  Purchase #4 $187.50   9.225%   $204.7969   $204.80   $204.80   $204.80  
  Purchase #5 $55.60   12.440%   $62.5166   $62.52   $62.50   $62.50  
  Purchase #6 $210.36   9.148%   $229.6037   $229.60   $229.60   $229.60  
  Purchase #7 $238.84   11.293%   $265.8122   $265.81   $265.80   $265.80  
  7 purchase totals = $1,178.37       $1,294.7092   $1,294.71   $1,294.70   $1,294.70