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 $61.89   11.199%   $68.8211   $68.82   $68.80   $68.80  
  Purchase #2 $119.48   13.146%   $135.1868   $135.19   $135.20   $135.20  
  Purchase #3 $205.68   12.222%   $230.8182   $230.82   $230.80   $230.80  
  Purchase #4 $93.83   7.273%   $100.6543   $100.65   $100.65   $100.70  
  Purchase #5 $22.88   6.746%   $24.4235   $24.42   $24.40   $24.40  
  Purchase #6 $209.85   6.295%   $223.0601   $223.06   $223.05   $223.10  
  Purchase #7 $213.31   3.589%   $220.9657   $220.97   $220.95   $221.00  
  7 purchase totals = $926.92       $1,003.9297   $1,003.93   $1,003.85   $1,004.00