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 $113.70   11.751%   $127.0609   $127.06   $127.05   $127.10  
  Purchase #2 $173.89   12.131%   $194.9846   $194.98   $195.00   $195.00  
  Purchase #3 $39.46   4.276%   $41.1473   $41.15   $41.15   $41.10  
  Purchase #4 $89.49   4.295%   $93.3336   $93.33   $93.35   $93.30  
  Purchase #5 $12.36   11.647%   $13.7996   $13.80   $13.80   $13.80  
  Purchase #6 $53.67   6.352%   $57.0791   $57.08   $57.10   $57.10  
  Purchase #7 $94.32   8.776%   $102.5975   $102.60   $102.60   $102.60  
  7 purchase totals = $576.89       $630.0026   $630.00   $630.05   $630.00