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 $69.62   5.782%   $73.6454   $73.65   $73.65   $73.60  
  Purchase #2 $212.52   3.780%   $220.5533   $220.55   $220.55   $220.60  
  Purchase #3 $178.73   6.130%   $189.6861   $189.69   $189.70   $189.70  
  Purchase #4 $14.55   12.384%   $16.3519   $16.35   $16.35   $16.40  
  Purchase #5 $76.35   4.243%   $79.5895   $79.59   $79.60   $79.60  
  Purchase #6 $57.99   7.123%   $62.1206   $62.12   $62.10   $62.10  
  Purchase #7 $61.47   5.758%   $65.0094   $65.01   $65.00   $65.00  
  7 purchase totals = $671.23       $706.9562   $706.96   $706.95   $707.00