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 $108.45   11.539%   $120.964   $120.96   $120.95   $121.00  
  Purchase #2 $147.31   4.751%   $154.3087   $154.31   $154.30   $154.30  
  Purchase #3 $52.44   12.148%   $58.8104   $58.81   $58.80   $58.80  
  Purchase #4 $56.74   9.173%   $61.9448   $61.94   $61.95   $61.90  
  Purchase #5 $165.95   6.228%   $176.2854   $176.29   $176.30   $176.30  
  Purchase #6 $153.28   4.677%   $160.4489   $160.45   $160.45   $160.40  
  Purchase #7 $62.93   13.144%   $71.2015   $71.20   $71.20   $71.20  
  7 purchase totals = $747.10       $803.9637   $803.96   $803.95   $803.90