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 $247.85   10.410%   $273.6512   $273.65   $273.65   $273.70  
  Purchase #2 $246.88   7.236%   $264.7442   $264.74   $264.75   $264.70  
  Purchase #3 $207.42   6.442%   $220.782   $220.78   $220.80   $220.80  
  Purchase #4 $107.64   8.521%   $116.812   $116.81   $116.80   $116.80  
  Purchase #5 $71.87   6.288%   $76.3892   $76.39   $76.40   $76.40  
  Purchase #6 $163.79   9.352%   $179.1076   $179.11   $179.10   $179.10  
  Purchase #7 $67.57   8.755%   $73.4858   $73.49   $73.50   $73.50  
  7 purchase totals = $1,113.02       $1,204.9720   $1,204.97   $1,205.00   $1,205.00