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 $161.59   7.251%   $173.3069   $173.31   $173.30   $173.30  
  Purchase #2 $188.70   12.237%   $211.7912   $211.79   $211.80   $211.80  
  Purchase #3 $128.32   7.746%   $138.2597   $138.26   $138.25   $138.30  
  Purchase #4 $62.53   13.559%   $71.0084   $71.01   $71.00   $71.00  
  Purchase #5 $216.29   11.797%   $241.8057   $241.81   $241.80   $241.80  
  Purchase #6 $41.64   7.532%   $44.7763   $44.78   $44.80   $44.80  
  Purchase #7 $156.94   8.339%   $170.0272   $170.03   $170.05   $170.00  
  7 purchase totals = $956.01       $1,050.9754   $1,050.99   $1,051.00   $1,051.00