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 $54.59   11.445%   $60.8378   $60.84   $60.85   $60.80  
  Purchase #2 $138.66   12.500%   $155.9925   $155.99   $156.00   $156.00  
  Purchase #3 $138.99   12.461%   $156.3095   $156.31   $156.30   $156.30  
  Purchase #4 $126.42   5.789%   $133.7385   $133.74   $133.75   $133.70  
  Purchase #5 $113.29   6.215%   $120.331   $120.33   $120.35   $120.30  
  Purchase #6 $176.44   8.498%   $191.4339   $191.43   $191.45   $191.40  
  Purchase #7 $12.53   11.474%   $13.9677   $13.97   $13.95   $14.00  
  7 purchase totals = $760.92       $832.6109   $832.61   $832.65   $832.50