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 $204.93   5.651%   $216.5106   $216.51   $216.50   $216.50  
  Purchase #2 $229.96   11.182%   $255.6741   $255.67   $255.65   $255.70  
  Purchase #3 $148.51   11.512%   $165.6065   $165.61   $165.60   $165.60  
  Purchase #4 $97.99   3.774%   $101.6881   $101.69   $101.70   $101.70  
  Purchase #5 $45.84   7.869%   $49.4471   $49.45   $49.45   $49.40  
  Purchase #6 $52.52   6.544%   $55.9569   $55.96   $55.95   $56.00  
  Purchase #7 $218.26   6.308%   $232.0278   $232.03   $232.05   $232.00  
  7 purchase totals = $998.01       $1,076.9111   $1,076.92   $1,076.90   $1,076.90