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 $241.47   11.415%   $269.0338   $269.03   $269.05   $269.00  
  Purchase #2 $216.96   13.786%   $246.8701   $246.87   $246.85   $246.90  
  Purchase #3 $216.97   8.578%   $235.5817   $235.58   $235.60   $235.60  
  Purchase #4 $110.72   5.534%   $116.8472   $116.85   $116.85   $116.80  
  Purchase #5 $65.35   12.346%   $73.4181   $73.42   $73.40   $73.40  
  Purchase #6 $196.52   6.476%   $209.2466   $209.25   $209.25   $209.20  
  Purchase #7 $111.78   8.721%   $121.5283   $121.53   $121.55   $121.50  
  7 purchase totals = $1,159.77       $1,272.5258   $1,272.53   $1,272.55   $1,272.40