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 $83.36   12.274%   $93.5916   $93.59   $93.60   $93.60  
  Purchase #2 $105.69   9.635%   $115.8732   $115.87   $115.85   $115.90  
  Purchase #3 $202.47   4.553%   $211.6885   $211.69   $211.70   $211.70  
  Purchase #4 $233.64   8.645%   $253.8382   $253.84   $253.85   $253.80  
  Purchase #5 $163.84   9.300%   $179.0771   $179.08   $179.10   $179.10  
  Purchase #6 $217.60   11.837%   $243.3573   $243.36   $243.35   $243.40  
  Purchase #7 $107.69   13.595%   $122.3305   $122.33   $122.35   $122.30  
  7 purchase totals = $1,114.29       $1,219.7564   $1,219.76   $1,219.80   $1,219.80