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 $120.94   3.278%   $124.9044   $124.90   $124.90   $124.90  
  Purchase #2 $204.40   8.787%   $222.3606   $222.36   $222.35   $222.40  
  Purchase #3 $244.69   9.192%   $267.1819   $267.18   $267.20   $267.20  
  Purchase #4 $150.74   7.249%   $161.6671   $161.67   $161.65   $161.70  
  Purchase #5 $159.60   4.825%   $167.3007   $167.30   $167.30   $167.30  
  Purchase #6 $124.29   9.298%   $135.8465   $135.85   $135.85   $135.80  
  Purchase #7 $13.96   3.133%   $14.3974   $14.40   $14.40   $14.40  
  7 purchase totals = $1,018.62       $1,093.6586   $1,093.66   $1,093.65   $1,093.70