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 $34.98   6.123%   $37.1218   $37.12   $37.10   $37.10  
  Purchase #2 $154.30   3.635%   $159.9088   $159.91   $159.90   $159.90  
  Purchase #3 $134.38   11.873%   $150.3349   $150.33   $150.35   $150.30  
  Purchase #4 $242.45   9.821%   $266.261   $266.26   $266.25   $266.30  
  Purchase #5 $242.61   6.618%   $258.6659   $258.67   $258.65   $258.70  
  Purchase #6 $189.92   8.497%   $206.0575   $206.06   $206.05   $206.10  
  Purchase #7 $52.78   6.514%   $56.2181   $56.22   $56.20   $56.20  
  7 purchase totals = $1,051.42       $1,134.5680   $1,134.57   $1,134.50   $1,134.60