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 $54.25   12.654%   $61.1148   $61.11   $61.10   $61.10  
  Purchase #2 $181.49   12.729%   $204.5919   $204.59   $204.60   $204.60  
  Purchase #3 $241.62   10.225%   $266.3256   $266.33   $266.35   $266.30  
  Purchase #4 $244.55   10.820%   $271.0103   $271.01   $271.00   $271.00  
  Purchase #5 $248.96   8.712%   $270.6494   $270.65   $270.65   $270.60  
  Purchase #6 $45.74   7.337%   $49.0959   $49.10   $49.10   $49.10  
  Purchase #7 $217.82   13.172%   $246.5113   $246.51   $246.50   $246.50  
  7 purchase totals = $1,234.43       $1,369.2992   $1,369.30   $1,369.30   $1,369.20