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 $60.86   12.647%   $68.557   $68.56   $68.55   $68.60  
  Purchase #2 $156.72   7.580%   $168.5994   $168.60   $168.60   $168.60  
  Purchase #3 $245.94   4.802%   $257.75   $257.75   $257.75   $257.80  
  Purchase #4 $41.45   12.289%   $46.5438   $46.54   $46.55   $46.50  
  Purchase #5 $128.47   3.151%   $132.5181   $132.52   $132.50   $132.50  
  Purchase #6 $84.84   7.753%   $91.4176   $91.42   $91.40   $91.40  
  Purchase #7 $79.57   3.862%   $82.643   $82.64   $82.65   $82.60  
  7 purchase totals = $797.85       $848.0289   $848.03   $848.00   $848.00