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 $34.71   6.788%   $37.0661   $37.07   $37.05   $37.10  
  Purchase #2 $54.68   3.221%   $56.4412   $56.44   $56.45   $56.40  
  Purchase #3 $101.50   12.191%   $113.8739   $113.87   $113.85   $113.90  
  Purchase #4 $151.78   9.728%   $166.5452   $166.55   $166.55   $166.50  
  Purchase #5 $226.52   5.872%   $239.8213   $239.82   $239.80   $239.80  
  Purchase #6 $250.86   5.372%   $264.3362   $264.34   $264.35   $264.30  
  Purchase #7 $129.64   3.517%   $134.1994   $134.20   $134.20   $134.20  
  7 purchase totals = $949.69       $1,012.2833   $1,012.29   $1,012.25   $1,012.20