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 $78.51   13.298%   $88.9503   $88.95   $88.95   $89.00  
  Purchase #2 $155.92   3.490%   $161.3616   $161.36   $161.35   $161.40  
  Purchase #3 $205.98   13.122%   $233.0087   $233.01   $233.00   $233.00  
  Purchase #4 $65.62   3.580%   $67.9692   $67.97   $67.95   $68.00  
  Purchase #5 $149.69   13.701%   $170.199   $170.20   $170.20   $170.20  
  Purchase #6 $63.82   8.400%   $69.1809   $69.18   $69.20   $69.20  
  Purchase #7 $220.29   5.120%   $231.5688   $231.57   $231.55   $231.60  
  7 purchase totals = $939.83       $1,022.2385   $1,022.24   $1,022.20   $1,022.40