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 $63.52   11.210%   $70.6406   $70.64   $70.65   $70.60  
  Purchase #2 $219.92   11.744%   $245.7474   $245.75   $245.75   $245.70  
  Purchase #3 $165.67   11.251%   $184.3095   $184.31   $184.30   $184.30  
  Purchase #4 $219.29   4.808%   $229.8335   $229.83   $229.85   $229.80  
  Purchase #5 $152.45   5.726%   $161.1793   $161.18   $161.20   $161.20  
  Purchase #6 $77.36   7.407%   $83.0901   $83.09   $83.10   $83.10  
  Purchase #7 $224.73   3.677%   $232.9933   $232.99   $233.00   $233.00  
  7 purchase totals = $1,122.94       $1,207.7937   $1,207.79   $1,207.85   $1,207.70