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 $81.32   8.245%   $88.0248   $88.02   $88.00   $88.00  
  Purchase #2 $197.35   6.207%   $209.5995   $209.60   $209.60   $209.60  
  Purchase #3 $203.91   4.467%   $213.0187   $213.02   $213.00   $213.00  
  Purchase #4 $199.87   6.300%   $212.4618   $212.46   $212.45   $212.50  
  Purchase #5 $218.37   4.586%   $228.3844   $228.38   $228.40   $228.40  
  Purchase #6 $223.73   3.155%   $230.7887   $230.79   $230.80   $230.80  
  Purchase #7 $157.72   12.694%   $177.741   $177.74   $177.75   $177.70  
  7 purchase totals = $1,282.27       $1,360.0189   $1,360.01   $1,360.00   $1,360.00