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 $26.98   8.518%   $29.2782   $29.28   $29.30   $29.30  
  Purchase #2 $168.77   11.409%   $188.025   $188.03   $188.05   $188.00  
  Purchase #3 $97.67   4.780%   $102.3386   $102.34   $102.35   $102.30  
  Purchase #4 $219.62   5.799%   $232.3558   $232.36   $232.35   $232.40  
  Purchase #5 $174.67   10.828%   $193.5833   $193.58   $193.60   $193.60  
  Purchase #6 $229.61   9.170%   $250.6652   $250.67   $250.65   $250.70  
  Purchase #7 $21.72   10.402%   $23.9793   $23.98   $24.00   $24.00  
  7 purchase totals = $939.04       $1,020.2254   $1,020.24   $1,020.30   $1,020.30