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 $243.96   10.602%   $269.8246   $269.82   $269.80   $269.80  
  Purchase #2 $43.29   3.280%   $44.7099   $44.71   $44.70   $44.70  
  Purchase #3 $181.51   10.180%   $199.9877   $199.99   $200.00   $200.00  
  Purchase #4 $145.78   10.498%   $161.084   $161.08   $161.10   $161.10  
  Purchase #5 $31.54   12.873%   $35.6001   $35.60   $35.60   $35.60  
  Purchase #6 $84.54   4.694%   $88.5083   $88.51   $88.50   $88.50  
  Purchase #7 $110.74   13.787%   $126.0077   $126.01   $126.00   $126.00  
  7 purchase totals = $841.36       $925.7223   $925.72   $925.70   $925.70