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 $85.36   12.597%   $96.1128   $96.11   $96.10   $96.10  
  Purchase #2 $196.71   3.609%   $203.8093   $203.81   $203.80   $203.80  
  Purchase #3 $196.95   11.374%   $219.3511   $219.35   $219.35   $219.40  
  Purchase #4 $143.34   4.307%   $149.5137   $149.51   $149.50   $149.50  
  Purchase #5 $123.33   11.682%   $137.7374   $137.74   $137.75   $137.70  
  Purchase #6 $157.65   11.176%   $175.269   $175.27   $175.25   $175.30  
  Purchase #7 $111.52   13.434%   $126.5016   $126.50   $126.50   $126.50  
  7 purchase totals = $1,014.86       $1,108.2949   $1,108.29   $1,108.25   $1,108.30