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 $194.39   4.269%   $202.6885   $202.69   $202.70   $202.70  
  Purchase #2 $121.45   11.387%   $135.2795   $135.28   $135.30   $135.30  
  Purchase #3 $93.55   3.641%   $96.9562   $96.96   $96.95   $97.00  
  Purchase #4 $52.98   6.618%   $56.4862   $56.49   $56.50   $56.50  
  Purchase #5 $180.75   13.187%   $204.5855   $204.59   $204.60   $204.60  
  Purchase #6 $145.45   11.816%   $162.6364   $162.64   $162.65   $162.60  
  Purchase #7 $168.42   3.441%   $174.2153   $174.22   $174.20   $174.20  
  7 purchase totals = $956.99       $1,032.8476   $1,032.87   $1,032.90   $1,032.90