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 $126.75   6.139%   $134.5312   $134.53   $134.55   $134.50  
  Purchase #2 $11.50   12.551%   $12.9434   $12.94   $12.95   $12.90  
  Purchase #3 $40.52   7.279%   $43.4695   $43.47   $43.45   $43.50  
  Purchase #4 $72.40   9.114%   $78.9985   $79.00   $79.00   $79.00  
  Purchase #5 $228.64   6.456%   $243.401   $243.40   $243.40   $243.40  
  Purchase #6 $139.27   6.187%   $147.8866   $147.89   $147.90   $147.90  
  Purchase #7 $41.97   4.859%   $44.0093   $44.01   $44.00   $44.00  
  7 purchase totals = $661.05       $705.2395   $705.24   $705.25   $705.20